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Appendix VL                          1133

100 /0. It is clear, however, that if the two engines are con-
sidered as one, the energy B that is rejected on direct working is
simply returned on reversal, the work given up at C being used
to effect that reversal.

When the reversed engine or heat pump is applied to re-
frigeration, it is as a heat extractor and not as a heat supplier
that it becomes useful. Then, adopting a new term instead of
' efficiency,'

Co-efficient of \ ___  Heat extracted __ B ___    r2     __ 9

Performance j ~~ work expended ~~ C " r1r~2~~' 7 say'

In the two diagrams, Fig. 1002, A is a radiator and AX an
absorber of heat to or from the outside air, while B B are
expanding and c c compressing pistons only, worked from the
engines E E. The valves are so arranged as to cause the
enclosed air to move in the direction of the arrows.

In the left diagram the air is compressed by c to a high
temperature and passed on to the radiator A, where the heat is
given to the outer air. It is next expanded in B, doing work on
the crank, and, falling in temperature, enters the chamber in the
cold condition.

In the right diagram the air is expanded in B below the out-
side temperature, and passing through At absorbs heat from the
outer air. It is next compressed in c to a higher temperature,
and enters the chamber in the hot condition. The first is a means
of cooling, and the second of heating the air of a chamber or
room, and,

For d}
	Jtieat extracted  __

For (2} ......
	work done Heat delivered
	ri  r2


This method of heating, suggested by Kelvin in 1852, by
which the coal, instead of being burnt in a fireplace, supplies a
boiler, direct engine, and heat-pump in series, can be made to
return more energy from the outer air than is rejected thereto,
as follows:

Referring again to Fig. 1001, it has already been shewn that if
the direct and reversed engines are coupled, while receiving and
delivering heat through the same temperature ranges, the received